proceedings of the polytechnic association. 567 



The Art of Tanning. 



Mr. Tlioinas Sm;ill opened the discussion on this subject by some general 

 statements regarding- the importance of the art. The processes used liave 

 not generally kept pace with scientiSc knowledge, relating to the chemical 

 re-actions employed to produce leather. In England, and in some parts of 

 this countr}', tlie same methods have been used for the last fifty years. 

 Col. Edwards was the first to introduce the mode of pumping and heating 

 the liquid extract of the bark. This increases the action, but heat above 

 the boiling point, injures the leather. Within my own time the plan of 

 obtaining the extract of hemlock bark and transporting it to this city and 

 applying it to hides, was thorouglily tried. It did not make good leather, 

 and was not economical, because the dry hide increases in weight when 

 turned into leather, and it is cheaper to take the hides to the neigliborhood 

 of the hemlock forests and return them to the city, than to bring the bark 

 to the city, or to subject it to the process of boiling down in the forest, and 

 bringing it in barrels to New York. It requires about 2,000 pounds of 

 bark to tan 170 pounds of leather. 



Some six or eight years ago, a gentleman by the name of Steel, came 

 from the West to this city, with an idea that in the ordinary mode of 

 leaching, there was a certain amount of tannin still left in the bark. He 

 took the spent bark that used to be thrown away, and extracted from it 

 some fourteen degrees by the barkometer, of extra strength. This result 

 "was so extraordinary that no leather manufacturer would believe it. 

 About a year and a half ago, Mr. Pinkney took up the matter of u&ing 

 spent bark. He made a tank with a false bottom in it, in which he placed 

 the hides, and poured the hot liquor down on them, and produced very 

 astonishing results. By the process of Rdwards, however, the best results 

 have been obtained. One hundred and ninety pounds of leather are made 

 from ninety pounds of hide. The average of Buenos Ayres leather will 

 make for every one hundred pounds, one hundred and eighty pounds of 

 leather. The leather trade in this country, particularly the sole leather, is 

 as good as any made in the world, and although we make more leather 

 than any other nation, still we import considerable. Sole leather can be 

 tanned in three months, but a longer time is considered advantageous. 

 The amount of hemlock bark is decreasing rapidly by the cutting down of 

 forests, and it is an interesting question whether the spent bai-k can be 

 used over economically. A patent obtained for-it has been sold for twenty- 

 five thousand dollars, and the process is said to' be profitable. 



About 10,000,000 of sides of leather, weighing 180,000,000 pounds are 

 annually made in the city of New York. It may be interesting to know 

 that this city buys more hides "and sells more leather than the cities of 

 London, Liverpool and Paris together. Hemlock bark is principally used 

 in this country, the trees from about 70,000 acres of land are cut every 

 year to supply this demand. As the hemlock does not grow again on the 

 same land, it becomes important to know from what quarter this supply is 

 to come in the future. Hemlock bark is limited to the States of New York, 

 Pennsylvania, Maine, Michigan, Wisconsin and Iowa. The hemlock forests 

 in these States are estimated together at about 200 miles square. In 40 



